Estimation of the net acid load of the diet of ancestral preagricultural Homo sapiens

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INTRODUCTION:

The nutritional requirements of Homo sapiens—the only extant species of the 5–7-million-year-old hominid family and its most recently evolved member (< 200 000 y old)—were established by natural selection during millions of years in which its hominid ancestors, including earlier Homo species, consumed foods exclusively from a menu of wild animals and uncultivated plants (1 –3 ). The profound transformation of the ancestral diet 10 000 y ago resulting from the inventions of agriculture and animal husbandry and, more recently, by industrial-scale food production and distribution technologies has provided natural selection an enormous challenge to eliminate the inevitable resulting maladaptations but has afforded it too little time—< 1% of hominid evolutionary time—to do so (1 , 3 –6 ).

In comparison with the diet habitually ingested by preagricultural Homo sapiens living in the Upper Paleolithic period (40 000–10 000 y ago), the diet of contemporary Homo sapiens is rich in saturated fat, simple sugars, sodium, and chloride and poor in fiber, magnesium, and potassium (1 , 2 ). These and numerous other postagricultural dietary compositional changes have been implicated as risk factors in the pathogenesis of "diseases of civilization," including atherosclerosis, hypertension, type 2 diabetes, osteoporosis, and certain types of cancer (7 –13 ).

One characteristic of the contemporary human diet for which no quantitative comparison has been made with the inferred ancestral preagricultural diet is its imbalance of nutrient precursors of hydrogen and bicarbonate ions, resulting in the body’s net production of noncarbonic acid, ranging over an order of magnitude from 10 to 150 mEq/d among diets (14 –17 ). Although multiple homeostatic mechanisms operate to mitigate the resulting deviations in systemic acid-base equilibrium, on average, blood acidity remains increased and plasma bicarbonate concentrations decreased in proportion to the magnitude of the daily net acid load (15 , 16 ). Increasing evidence has been adduced that suggests that such persisting, albeit low-grade, acidosis, and the relentless operation of responding homeostatic mechanisms, result in numerous injurious effects on the body, including dissolution of bone, muscle wasting, kidney stone formation, and damage to the kidney (18 –23 ).

In this article we report estimates of net endogenous acid production (NEAP)—the net acid load of the diet—for 159 retrojected prehistoric preagricultural diets of Homo sapiens and their hominid ancestors. In contrast with the characteristically net acid-producing contemporary diet, most such retrojected ancestral diets were net base-producing, and we detail the characteristics that made them so.